Volatile capital flows pose perpetual challenges for surveillance, policymaking, and investing, notably in ASEAN+3 emerging market economies. Hence, the ability to monitor these flows on a timely basis and assess the vulnerability of equity and debt markets to sell-offs by non-resident (NR) investors are crucial. The objective of this paper is twofold: First, we construct a timely, high-frequency database of NR portfolio flows for ASEAN+3 economies by identifying and transparently stitching together relevant official series. And then, we use the data to develop a framework for assessing risks of sudden outflows. Our analysis reveals that ASEAN+3 markets with larger NR investor positions tend to be more sensitive to changes in global asset prices and yields, and there is evidence that positioning affects the size of NR portfolio outflows during episodes of market stress. However, this work is preliminary, and further and more rigorous research are necessary to develop a more comprehensive framework for analyzing short-term capital flows.